A trunnion of the above type for mounting a rocker arm is known from DE-U 19 38 943 and comprises a surface which is parallel to the central axis of the trunnion and constitutes a bearing surface for a fixing screw which is inserted through a bore perpendicular to the central axis. The screw head or the retaining nut of the screw bears against the bearing surface. It is also known in the art to make such trunnions as rotationally non-symmetrical parts with bearing surfaces by an upsetting procedure. A drawback of this method is that, due to an insufficient flux of material during the forming process, the bearing surface is inadequately configured, i.e. it slopes downwards towards its edges leaving a smaller effective bearing surface for the fixing screw. A remedy for this is sought in milling flat the bearing surface but this is an additional work step which increases the manufacturing costs. A further drawback is that a bearing surface post-milled in this way experiences no increase in hardness, that is to say, it is too soft.